Prior to the present invention, polymethoxyhydrosilanes having the formula, ##STR1## where R is selected from C.sub.(1-13) monovalent hydrocarbon radicals and substituted C.sub.(1-13) monovalent hydrocarbon radicals and a has a value of 0 or 1, were prepared in a batch process by reacting polychlorohydrosilane of the formula, ##STR2## with methanol, as shown by F. Taurke, Ber. 38 1661 (1905), M. E. Havill, I. Joffe and H. W. Post, J. Org. Chem. 13 289 (1948), Ger. Offen. No. 2,409,731 and H. J. Kotzch et al U.S. Pat. No. 4,228,092. Although high yields of polymethoxyhydrosilanes of formula (1) can be obtained by such batch procedures, experience has shown that such methods cannot be extended to a continuous process due to various side reactions which often results in the loss of hydrogen bonded to silicon.
The present invention is based on my discovery that if methanol is allowed to contact polychlorohydrosilane vapor and the resulting hydrogen chloride is immediately separated from the polymethoxysilane reaction product, polymethoxyhydrosilane can be made at high yields. A preferred procedure is to effect contact between methanol and polychlorohydrosilane vapor in a vertical reactor such as shown by the drawing, allowing for the separation of a polymethoxysilane bottoms product, and the recovery of the desired polymethoxyhydrosilane as a distillation product.